In recent years, a laser engraving method has been used in surface treatment for printing such as flexographic printing and dry offset printing in which resin relief printing plates are used, and that for embossing. The laser engraving method is a method for forming a relief and projection pattern on a surface by removing a part of a resin irradiated with a laser beam.
Example of materials used for the laser engraving method include vulcanized rubbers, cured products of photosensitive resins obtained by photo-curing a photosensitive resin composition, and cured products of thermosetting resins obtained by curing a thermosetting resin composition by heat treatment. A technique to perform laser engraving on a cured product of a photosensitive resin has been increasingly used from the viewpoint of reduction in processing time.
Conventionally, printing plates have been produced by a pattern forming method using a sheet-like photosensitive resin original plate and a photomechanical processing technique or a pattern forming method using a sheet-like resin original plate and a laser engraving technique. However, a technique for producing a printing sleeve has been developed for demands such as reduction in a time for registration during a printing step, reduction in an amount of unnecessary printed matters by reducing a printing adjustment time, and high-speed printing.
In the pattern forming method using the photomechanical processing technique, in the case where a metallic cylinder or a light-intransmissive cylindrical support made of a fiber reinforced plastic is used, back exposure (solid exposure from a rear surface of the blank printing sleeve through a light-transmissive sheet-like support) necessary for production of a printing sleeve base serving as foundation of the pattern is difficult. For that reason, pattern formation is insufficient so that printing quality is affected. The photomechanical processing technique needs complicated processing such as exposure, development, and drying. Furthermore, a configuration of the blank printing sleeve is also complicated: for example, in order to form a pattern based on digital data, a step of laminating a black thin film for producing an exposure mask by burning off a printing sleeve surface with near-infrared laser is needed.
On the other hand, the pattern forming method using the laser engraving technique can form a pattern on a surface of a resin plate freely by engraving by laser. Because the digital data can be directly processed with a laser engraving apparatus, the laser engraving technique has no problem mentioned above, and attracts attention as a method for producing a printing sleeve.
In a printing technique for narrow web, dry offset can printing, and the like in the flexographic printing, narrow printing plates are used.
Furthermore, in the field of the flexographic printing, hollow cylindrical supports made of a fiber reinforced plastic are used for an increasing demand for high-speed printing properties. Patent Document 1 discloses a laser engraving blank printing sleeve made of a thermoplastic elastomer as a main raw material and obtained by molding a sheet-like photosensitive resin into a cylindrical shape.
Patent Document 2 discloses a method for producing a blank printing sleeve using a liquid photosensitive resin.
Patent Document 3 discloses a method for producing a printing original plate by a cutting step of dividing a blank printing sleeve into some specified blank printing sleeves.